1. Field of the Invention
The present invention relates to a throttle valve control apparatus which is connected to a predetermined equipment including, for example, an intake manifold of an internal combustion engine. Specifically, the present invention relates to a throttle valve control apparatus to which a purge control valve is directly connected.
2. Description of the Related Art
In general, evaporating fuel is generated in a fuel tank for storing fuel to be used to drive an engine. However, the evaporating fuel emitted to the atmospheric air causes the atmospheric pollution. Therefore, the evaporating fuel is purged (aspirated) to an intake passage which is formed in a main throttle body of a throttle valve control apparatus communicating with a cylinder chamber of the engine so that the evaporating fuel may be combusted together with the air-fuel mixture.
For purging the evaporating fuel to the intake passage, a method is known in which the evaporating fuel generated in the fuel tank is once adsorbed to a canister composed of activated carbon and, then, the fuel adsorbed to the canister is purged to the intake passage during a loading operation of the engine under the control of a purge control valve. In this case, the purge control valve and the throttle valve control apparatus are connected to one another by a piping. Further, in order to make communication between the piping and the intake passage, a purge hole having a small diameter is formed on a surface parallel to a throttle shaft to which a throttle valve of a main throttle body is fixed and held. That is, when the throttle valve of the throttle valve control apparatus is opened, the evaporating fuel is purged through the purge hole to the intake passage in accordance with the aspirating pressure of air flowing through the intake passage.
In the above conventional technique, the purge control valve and the throttle valve control apparatus are connected to one another by the piping. Therefore, it is necessary for the evaporating fuel to flow over a distance corresponding to the length of the piping during a period ranging from the opening of the throttle valve of the throttle valve control apparatus until the evaporating fuel is purged to the intake passage under the control of the purge control valve. A long period of time is needed until the evaporating fuel arrives at the intake passage corresponding thereto. In other words, the following inconvenience arises that the evaporating fuel is not purged to the intake passage quickly after the throttle valve is opened, thereby resulting in unsatisfactory response performance with respect to the operation of the throttle valve.
Furthermore, the purge hole having the small diameter is formed on the surface parallel to the throttle shaft of the main throttle body. Therefore, the distance between the throttle valve and the outlet of the purge hole (communicating portion with respect to the intake passage) varies depending on the opening/closing operation of the throttle valve. The pressure is also fluctuated in the vicinity of the outlet of the purge hole. In addition thereto, the purge amount of the evaporating fuel varies. Accordingly, the problem arises that it is impossible to reliably purge the evaporating fuel generated in the fuel tank to the intake passage. Furthermore, it is difficult to purge the evaporating fuel at a sufficient flow rate because the purge hole has the small diameter.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a throttle valve control apparatus which makes it possible to quickly purge the evaporating fuel in response to the operation of a throttle valve, and which makes it possible to reliably purge the evaporating fuel at a desired flow rate without being affected by the opening/closing operation of the throttle valve.
According to the present invention, there is provided a throttle valve control apparatus provided with a purge control valve for controlling a flow rate of evaporating fuel to be purged to an intake passage formed in a main throttle body; wherein the purge control valve is directly connected to a surface which is substantially parallel to a throttle shaft of the main throttle body; and wherein a discharge nozzle of the purge control valve communicates with a purge passage which is formed on an end surface of the intake passage of the main throttle body in an axial direction, and a communicating section between the intake passage and the purge passage is provided at the inside of a wall surface of the main throttle body which holds the throttle shaft.
In the above arrangement, it is unnecessary to provide any piping for connecting the purge control valve and the throttle valve control apparatus. Therefore, the distance between the discharge nozzle of the purge control valve and the intake passage formed in the main throttle body of the throttle valve control apparatus can be shortened as short as possible. Accordingly, it is possible to quickly purge the evaporating fuel to the intake passage in response to the operation of the throttle valve.
Furthermore, the discharge nozzle of the purge control valve communicates with the intake passage via the purge passage, and the communicating section between the purge passage and the intake passage is located in the vicinity of the throttle shaft. Therefore, the distance between the throttle valve and the outlet of the purge passage (communicating section with respect to the intake passage) does not vary, which would be otherwise caused if the throttle valve performs the opening/closing action. Accordingly, the outlet of the purge passage can be prevented, as less as possible, from being affected by the pressure fluctuation due to the opening/closing action of the throttle valve. As a result, it is possible to reliably purge the evaporating fuel at a desired flow rate.
Furthermore, because the purge passage is formed on the end surface of the intake passage of the main throttle body in the axial direction, the purge passage can be simultaneously formed when, for example, the main throttle body is formed by means of die casting. Therefore, it is unnecessary to form the purge passage by applying machining processes such as drilling or the like after the main throttle body is formed. Accordingly, it is easy to form the purge passage.
In the throttle valve control apparatus constructed above, it is preferable that the purge passage is formed to have a circular arc-shaped configuration having a substantially constant width along an outer circumference of the intake passage for the following reason. The purge passage communicating with the intake passage has a predetermined volume unlike the conventional purge hole having the small diameter. Therefore, it is possible to reliably purge the evaporating fuel at a desired flow rate.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.